Figure 2.

Cardiomyocyte cell line HL-1 infection with the Daniels (DA) strain of TMEV (33, 42). (A) Confluent HL-1 cell monolayer infected with TMEV at a multiplicity of infection (MOI) = 10 showed no changes at 4 hours (h) post-inoculation (p.i.). Cytopathic effect (CPE), including the rounding up and detachment of cells from the culture dish, was observed at 12 h p.i., which developed cell lysis in most cells at 36 h p.i. (B) HL-1 cells and neuroblastoma cell line Neuro-2a were infected with TMEV at an MOI = 1 or 10. Cell viability was determined with trypan blue dye exclusion assays. Cell viability of both HL-1 and Neuro-2a cells decreased at 12 h p.i. and most cells died at 36 h p.i. (C) The concentration of cardiac troponin I in cell culture supernatants determined by an enzyme-linked immunosorbent assay (ELISA) was detectable in TMEV-infected HL-1 cells (open column), but not detectable (N.D.) in mock-infected HL-1 cells (closed column) or infected Neuro-2a cell culture (data not shown). (D) Viral titers of cell-free (•, ▴) and cell-associated virus (°, Δ) in HL-1 or Neuro-2a cell culture were determined by plaque assays with baby hamster kidney (BHK)-21 cells (24). In both HL-1 and Neuro-2a cells, cell-free virus titers increased substantially at 12 h p.i., while cell-associated viral titers increased at 8 h p.i. and peaked at 12 h p.i.